Various proposals have been made on a pneumatic tire which avoids a rapid decrease of its air pressure due to its puncture by disposing an adhesive sealant layer inside its tread portion for the purpose of securing safety for the vehicle in a case where the pneumatic tire runs over a nail while the vehicle is running.
An adhesive sealant is fluid. For this reason, if the adhesive sealant is exposed to the outside, a deflected flow occurs in the exposed adhesive sealant in the pneumatic tire while the pneumatic tire is in storage. In addition, the exposed adhesive sealant makes it difficult to mount the pneumatic tire onto a rim. With this taken into consideration, the surface of the adhesive sealant is usually covered with a cover rubber sheet for the purpose of avoiding these troubles.
When the pneumatic tire runs at high speed, the adhesive sealant flows and concentrates in the center area of the tire in the tire width direction due to the centrifugal force. In addition, the adhesive sealant is distributed unevenly in response to the tread portion's repeated change in shape on the contact side. The concentration and uneven distribution of the adhesive sealant reduces the tire's uniformity, and accordingly brings about problems including a problem that the reduced uniformity causes vibrations. Particularly in a case where the gauge thickness of the adhesive sealant layer is set larger for the purpose of securing the sealing effect, this phenomenon is conspicuously observed.
On the other hand, a proposal has been made on denaturation of an adhesive sealant layer into an adhesive and fluid sealant layer by using a rubber composition containing polyisobutylene rubber and peroxide for the adhesive sealant layer, disposing the rubber composition inside a tread portion of an uncured tire with the surface of the rubber composition being covered with a cover rubber sheet, and subsequently pyrolytically decomposing the rubber component with the peroxide by use of heat produced while the uncured tire is cured (see Patent Document 1, for example). Nevertheless, in the case of this type of tire, a large amount of cracked gas is produced while the rubber component is pyrolytically decomposed. For this reason, as shown in FIG. 5, the cracked gas G fills an interstice between the adhesive sealant layer 5 and the cover rubber sheet 6 so that the cover rubber seat 6 is distended. If the tire runs with the cover rubber sheet 6 distended by the cracked gas, the cover rubber sheet 6 blows out. This brings about a problem of further decreasing the uniformity of the tire.
Japanese Patent Application Kokai Publication No. 2003-80909